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A New Theorem Maps Out the Limits of Quantum Physics
- tus88 6y agoDoes the entanglement affect between particles propagate at the speed of light or instantaneous?
- andi999 6y agoNo affect propagates
- deleted 6y ago[deleted]
- Crash0v3rid3 6y agoSuppose you had two entangled particles light-years distance apart. Observer A observes one entangled particle at a spin up. At the same time, Observer B observes particle B at a spin down. Observer A's observation of a spin up means observer B must see a spin down. However, the two observers are restricted at the speed of light to communicate this to each other. It would initially seem like there is a instantaneous causal impact based on observer A's observation. But that's not the case. I tend to think it was predestined what each observer see, but that leads to all sorts of philosophical questions. I hope I did this topic justice, I find it quite interesting but have no background in it.
- annilt 6y agoThe article is about that. Bell inequalities proved there isn’t ‘predestined’ effect(If you mean ‘hidden variables’ by that)
- derbOac 6y agoBut isn't superdeterminism still possible? I thought that was implied by the article's first assumption that physics was loathe to abandon, that the experimenters had free will, so to speak.
- andreareina 6y agoIs superdeterminism even falsifiable?
- deleted 6y ago[deleted]
- fsh 6y agoNone of the interpretations of quantum mechanics are. By design, they all predict exactly the same outcome for any conceivable experiment. The subject is entirely philosophical, not scientific.
- andreareina 6y agoThey make predictions, which can be falsified. They even make different predictions---Scott Aaronson agrees that WF poses problems for the standard Copenhagen interpretation. Sean Carroll is on record somewhere saying that e.g. objective collapse models predict an in principle measurably different evolution of a system's entropy than many worlds. I suppose I should have asked what predictions SD actually makes.
- fsh 6y agoObjective-collapse theory is a modification of QM, not merely an interpretation. Superdeterminism on the other hand is not even a theory. It cannot be falsified by design.
- tsimionescu 6y agoCopenhagen Interpretation and MWI don't make different predictions from each other, but there are other theories that do. For example, pilot-wave theory makes different predictions. There are also some superdeterminist theories that make new predictions (Gerard T'Hooft is one advocate of such theories, I believe). Unfortunately I don't know of any concrete examples. Here is some more information on the subject from Sabine Hossenfelder: http://backreaction.blogspot.com/2019/07/the-forgotten-solution-superdeterminism.html?m=1 http://backreaction.blogspot.com/2019/07/the-forgotten-solut...
- andreareina 6y agoNo local hidden variables. Unless there's been a new development?
- annilt 6y agoYes, you’re right. I meant local hidden variables.
- andreareina 6y agoAww. I was hoping for a new development haha.
- alisonkisk 6y agoGlobal hidden variables are the predestined effect. The argument against global hidden variables is that it requires a godlike meddling in the whole universe to populate an infinite amount of arbitrary asymmetric details.
- annilt 6y agoAccepted as instant.
- Myto 6y agoThat's just false.
- annilt 6y agoThen explain it / give us a link please.
- Myto 6y agoWhy do I need to do that, to combat your unsupported assertion? Why don't you show some evidence instead that faster than light entanglement has been "accepted"? The fact is, there are theories of QM that do not assume that entanglement happens faster than light. The Many Worlds theory is one that has no need for such hypothesis. And more generally, since you need to send the results via a classical (no faster than light) communication method, there's no way to be sure that the entanglement has happened faster than light.
- deleted 6y ago[deleted]
- redlock 6y agohttps://physics.stackexchange.com/questions/15282/quantum-entanglement-faster-than-speed-of-light https://physics.stackexchange.com/questions/15282/quantum-en... And here is some experimental data http://arxiv.org/pdf/1303.0614v1.pdf http://arxiv.org/pdf/1303.0614v1.pdf
- mhh__ 6y agoThere is a so-called "no-go" theorem dealing with this. To actually collect information, you need to transmit data via some classical method i.e. the hou-c always wins
- d_tr 6y agoSystems get entangled with each other by interacting. So entanglement cannot "propagate" faster than the fastest possible "mediator" of an interaction, which is the speed of light. The "instantaneous" aspect comes up in entanglement and measurement. Say you start off with an entangled pair of electrons A and B in your lab, and measure electron A. Measurement is an interaction, so you become entangled with the electron. By knowing the initial entangled state and your reading of electron A's state, you can know stuff about the state of electron B at the time of the measurement, even if electron B has traveled a very long distance in the meantime. I personally find this point of view nicer than assuming that I somehow collapsed electron A's state and caused an instantaneous remote collapse of B's state.
- lostmsu 6y agoThis is just another take on Wigner's experiment. It is has more to do with philosophy, than physics. TL;DR; most probably you can't be sure what another person saw when they made a quantum measurement, because the person itself is a quantum system and therefore can be in a state of superposition of measuring A and measuring B.
- andreareina 6y agoMy reading of Scott Aaronson is that WF does have implications for the "standard" Copenhagen interpretation (ctrl-f many worlds). https://www.scottaaronson.com/blog/?p=3975 https://www.scottaaronson.com/blog/?p=3975
- mcherm 6y agoAs usual, Scott's take on it was far more comprehensible to me and more useful than the article itself.
- fungiblecog 6y agoThe problem is the insistence that there are two distinct particles that have an independent existence and properties. There isn't. There's just a quantum field which when it interacts with other fields in a measuring apparatus produces classical results in accordance with qm. Trying to understand what's really going on in terms of distinct and separate particles is never going to work.
- Ma8ee 6y agoOk, so skip the particles. Why does exactly one detector click?
- justnonsense 6y agoThe interaction of the detector with the field
- Ma8ee 6y agoThe emphasis of the question should be on “exactly one”. How does using fields instead of particles resolve the question of the collapse of the wave function?
- dash2 6y agoWhy are physicists reluctant to give up the idea of experimenter freedom, as the article says? Is there anything more to it than not wanting to deny free will?
- ddxxdd 6y agoIt's extremely unlikely that the universe compels scientists to make certain measurements at certain times in a conspiracy to make quantum physics look real. https://en.wikipedia.org/wiki/Superdeterminism https://en.wikipedia.org/wiki/Superdeterminism
- miltondts 6y agoWhy? All physics theories we have are deterministic.* So if we take that to the limit, then we are also deterministic. To me, there is nothing conspiratorial about that. *Yes, quantum mechanics is kind of debatable.. But if I understand it correctly, the actual theory is deterministic. It's just the interpretation of the measurements that can lead to some debate. However they can also be viewed in a deterministic framework, as the link you cite shows.
- DennisP 6y ago"We are deterministic" is no big deal, it's what scientists thought for centuries going back to Newton. In classical mechanics, if you knew the exact state of every particle then you could predict everything. But superdeterminism is nothing like that. It's determinism not based on past states, but based on future states, where the universe prevents anyone from making decisions that would cause them to learn a certain type of information. How would that work?
- miltondts 6y agoSuperdeterminism just says that there is no statical independence. Not sure where you are getting the future determines the past from that. However, yes, in a deterministic world there is only one way to get to a certain future, so I guess the future does indeed determine the past. Is that what you mean?
- EastLondonCoder 6y agoIt seems like some of the interpretations of quantum mechanics can be falsifiable with this method. Very Cool! In fact it looks like it would be possible to probe my favorite solution to the measurement problem: https://en.wikipedia.org/wiki/Objective-collapse_theory https://en.wikipedia.org/wiki/Objective-collapse_theory
- justnonsense 6y agoCould it be that each quantum is an encoded message or information that grows in a field called time. The quantum interacts with a universal machine, called universe that computes the result. So that the entaglement is only delayed computation, like in Haskell. So there is no problem understanding how the physics works, the universal machine is in a monad and we can only call return when the time is due. So I suggest considering space time as a delayed computation (more as a monad or time stated encoded) for a universal machine called our universe.
- justnonsense 6y agoWhat kind of computation machine is the universe? Could it be that a black hole is a loop, a recurrence call in this system. Could this be tested by forcing the machine to perform many delayed computation at once, line in a supernova ?, could it be that gravity and time measure the speed of computation of a local node?, can we design an experiment to count the number of local clusters of this machine?, is the computational power of this machine an input for the machine, i.e, it is self-regulated? Just nonsese.
- bondarchuk 6y ago>The third says that outcomes of measurements are absolute, objective facts for all observers. The key part of the argument that is (I feel) a bit obscured to make it sound more shocking, is the fact that "observers" here includes "observers who are themselves in a superposition state". Edit: the closing paragraph of the article is worse: >In which case, taking the position that an observation is subjective and valid only for a given observer — and that there’s no “view from nowhere” of the type provided by classical physics — may be a necessary and radical first step. I think that if you remember that they only proved this for "a given observer" that is itself in a superposition, it is a lot less "radical". PS I wrote another more elaborate comment about this research here https://news.ycombinator.com/item?id=24322949 https://news.ycombinator.com/item?id=24322949
- evanb 6y agoIndeed, it’s remarkable they want to make a fuss out of something that I can undo entirely via unitary transformation. There have been a number of papers with these kinds of “theorems” that seem to miss that proponents of the many-worlds interpretation would have explained (in this instance) Wigner’s friend in this way in the first place by eliminating all non-unitary evolution a priori.
- ur-whale 6y agoIt seems quantum mechanics systematically refuses to properly model the "observer". As in: mathematically quantum model of the large and complex experimental setup that tries to "measure" something, including the observer. It's probably not done because it's too hard, but the day they do this and actually include it in any equations that try to describe a system, I suspect much clarity will ensue.
- eigenket 6y agoIf you do that (at least with the approaches I've seen) and follow "standard" quantum mechanics rules for the observer as well as the observed the you end up deriving many worlds / Everettian quantum mechanics.
- d_tr 6y agoIt is AFAIK a very standard approach to treat two interacting quantum systems (e.g. two electrons) as "measuring" each other and work with density matrices and partial traces to see how the "measurement" is evolving and what is each system "seeing". You might be interested in learning about the field of quantum decoherence.
- alisonkisk 6y ago> Outcomes of measurements are absolute, objective facts for all observers. Seems easy to reject, it's just an extension of what Einstein's Relativity already showed (time is not objective), which is an extension of what Newton already formalized (velocity is not objective).